Conventionally, various improvements in configuration have been made for miniaturization and a high efficiency in the motor. For example, in a duplex feeding type squirrel cage induction motor, a technology is disclosed which intends to miniaturize the motor and to have a high efficiency by equalizing current densities of stator windings and rotor windings by equalizing an area ratio between stator slots and rotor slots (see patent document 1). According to this technology, equalizing the current density between the stator windings and the rotor windings relatively equalizes increase in temperature between the stator and the rotor. This can avoid decrease in a generation torque, so that it is possible to miniaturize the motor and to have a high efficiency in the squirrel cage induction motors. In addition, a technology is disclosed in which, by setting a slot area of the stator of a small-size capacitor type of induction motor to 0.45 to 0.65 of an area of a circle of which diameter is equal to a diameter of an outer diameter of the stator, a quantity of a used iron core can be reduced by 25% and a quantity of used conducting wires can be reduced by 18% for the same characteristic, and an output characteristic is increased by 145% for the same size (see patent document 2).